1. Field of the Invention:
This invention relates to a method of producing isotopically tailored zirconium. More specifically it deals with a method for the separation of one or more isotopes of zirconium out of the natural metal.
2. Description of the Prior Art:
Zirconium is used as a cladding material for nuclear fuel in nuclear reactors. This metal lends itself to this use because it has a low thermal neutron absorption as compared with other metals.
Zirconium as used in nuclear reactors contains 11% of isotope zirconium-91 which has over 8 times the thermal neutron absorption cross-section of the naturally occurring zirconium isotope mixture. Removal of this isotope would improve the usefulness of zirconium as a nuclear reactor fuel cladding material.
The above fact is noted by R. Dewitt, W. R. Wilkes and L. J. Wittenberg of Monsanto Research Corp., Mound Laboratory, Miamisburg, Ohio and stated in a published article entitled "Isotopically Tailored Materials For Fission And Fusion Reactors", MLM-2426 (OP), Conf-770566-1. In this article it further states:
"Zircaloy (98% zirconium, 2% tin) is presently used as the fuel cladding in the heavy-water-moderated power reactors, known as CANDU reactors, which are manufactured in Canada. Neutron absorption by this cladding material is the dominant neutron loss mechanism. Of the neutron absorption in the Zircaloy, nearly 60% occurs in the isotope zirconium-91, and 10% occurs in the impurity isotope hafnium-177. Critoph has suggested that optimizing the zirconium isotopes 90 and 94 in the Zircaloy cladding could improve the neutron economy, resulting in a reduction in the fuel loading of approximately 6% and increasing the conversion ratio in a uranium/thorium breeder by 5-6%. He has calculated the allowable cost for isotopically tailored Zircaloy containing less than 5% zirconium-91 could be as high as #1,000/kg in a non-breeder reactor (nearly 25 times the present cost) and up to $3,000/kg in a U/Th breeder."
The separation of zirconium isotopes would be roughly as expensive as the separation of U.sup.235 from U.sup.238, therefore, any process for production of isotopically tailored zirconium would have to provide very high yields to product after isotope separation. Present methods of chlorination and Kroll reduction of chlorides do not produce high enough yields to be practical.
The separation of isotopes by gaseous diffusion or centrifugation or calutron or laser separation requires a gaseous compound. ZrCl.sub.4 would not be satisfactory because chlorine has 2 stable isotopes which would interfere with separation. ZrF.sub.4 has been used for chemical reduction but is not a favorable material in that the reaction energy would be high making it difficult to reduce to metal. Fluoride salts also do not distill readily and are very toxic.
Although isotopically tailored zirconium is desired for the more efficient operation of nuclear reactors it is not at present commercially feasible because of the high cost of isotopic separation followed by low yield reductions by prior methods. An economic separation method is therefore needed in this field.